Unit tests - The benefit from unit tests with contract changes?

Question

Recently I had an interesting discussion with a colleague about unit tests. We were discussing when maintaining unit tests became less productive, when your contracts change.

Answer 1

Someone asked the same question in the Google Group for the book "Growing Object Oriented Software - Guided by Tests". The thread is Unit-test mock/stub assumptions rots.

Here is J.B. Rainsberger's answer (he is the author of Manning's "JUnit Recipes").